A disk drive is an information storage device. The most basic parts of a disk drive are an information storage disk that is rotated, an actuator that moves a slider carrying one or more transducers to various locations over the disk, and electrical circuitry that is used to write and read data to and from the disk. The one or more information storage disks are clamped to a rotating spindle. More specifically, storing data includes writing information representing the data to portions of tracks on a disk. The transducer includes two separate devices a write transducer that writes information representing data to the disk and a read transducer or sensor that reads information from the disk.
Storing data includes writing information representing the data to the disk. Conventional disk drives with magnetic media organize data in concentric tracks. There is a constant goal in these storage devices to store increased amounts of data. Two ways of increasing the storage capacity of these storage devices include increasing the bit density, which means reducing the spacing between individual bits along the circumference of a concentric track or a substantially concentric track. Another way to increase the capacity is to increase the track density. This involves writing the tracks more closely together.
Different recording technologies are most suited to different workloads and operating environments. At the time of manufacture or a disk drive, neither of these conditions may be known. In other words, at design or manufacturing time little if anything is known about the operating environment in which the disk drive will be placed. Customers purchase disk drives and place them into service. In addition, little is known about the workload that the disk drive will deal with in the operating environment.
Currently, there are many types of recording technologies in use. Each has advantages and disadvantages for different workloads and operating environments. Two common technologies are Perpendicular Magnetic Recording (“PMR”) and Shingled Magnetic Recording (“SMR”). Currently, the consumer purchases a disk drive that uses PMR or one that uses SMR. PMR can be written to any track on a disk drive that employs this technology. In other words, a disk drive using PMR technology can easily handle random writes and generally performs better than a disk drive using SMR without some sort of cache memory (on disk or solid state). The drawback is that the PMR disk drive will not be able to hold as much information representing data as an SMR disk drive. Shingled Magnetic Recording introduces the constraint that random writes may not be done in place. This is comes from the nature of the SMR head, which is wider than a nominal track. This type of recording works well in sequential write environments. SMR also works well when there is sufficient idle time to rewrite or ‘defrag’ writes that were not initially written ‘in place’. SMR provides a capacity boost which may approach 150% of a disk drive using PMR technology.
The write transducer or write element generally has a write width. The write width, in some instances, may produce a track with a width that is greater than it needs to be. In SMR, a portion of a previously written track is overwritten to produce tracks that are thinner or less wide. A portion of the original track is removed. The resultant track has a width thinner than the write width of a write element. The concept is referred as shingled writing.
Of course, one of the many goals for a disk drive is to increase capacity of a disk drive. Another of the many goals is to be able to recover or read the information that was previously written.